A sample has 128 radioactive nuclei. How many remain undecayed after 4 half-lives?
Answer and explanation
Correct answer: D. 8 nuclei
- Step 1: After half-lives . Answer: 8 nuclei. Why not the others: 32 nuclei: divides by the number of half-lives instead of . 16 nuclei: divides by twice the number of half-lives. 4 nuclei: uses one half-life too many.
Practise more Physics calculations.
Free questions with an explanation for every one, and full timed Medical Entrance Exam (University of Iceland) mock tests.
More Physics calculations questions
- A ball is thrown at 50 m/s at 45° to the ground. Taking m/s², what is its horizontal range?
- A simple pendulum has length 6.4 m. Taking m/s², what is its time period?
- Two point charges of 4 μC and 3 μC are placed 0.9 m apart in air. Taking N m²/C², what is the force between them?
- Capacitors of 4 μF and 6 μF are joined in series. What is the equivalent capacitance?
- How much energy is stored in a 10 μF capacitor charged to 10 V?
- Photons of energy 4 eV fall on a metal of work function 2.5 eV. What is the maximum kinetic energy of the emitted photoelectrons?